By David Wall, Mount Pleasant Master Gardener
This year, many are reconsidering raised bed vegetable gardens. The reasoning is simple. They’re compact, easy to work, easy to water, maintain moisture better, fewer problems with weeds, and usually produce more than a regular garden the same size. They come in all lengths, although widths are usually (not always) restricted to 4 feet.
Soil depth is extremely important. Raised beds that are only 4 inches tall work, but the effort combined with bed life makes them (for me) not worth the effort. Eight inches tall, which allows plenty of soil/ compost, should be the minimum height. Eight inches allows for adequate soil, compost and mulch for growing vegetables. Deep till the underlying soil, so future vegetable roots can go deeper if they need it. Layers of cardboard on top of the tilled area prevent weeds from penetrating. Well, if you have Bermuda grass, cardboard will at least slow it down!
The more height, the more room available to max out the garden’s ability to produce. My raised bed is 4 foot X 38 foot, and 24 inches tall, and made from three layers of concrete blocks. Twenty-four inches allows for construction of a hügelkultur garden. In the bottom is a layer of firewood, followed by 10-plus large bags of leaves. On top of this are several cubic yards of compost, topsoil and mulch. The bottom portion will take several years to totally decay, meaning additional fertilizers are not required. Initially overfill by at least 2 inches to account for settling. Also, raised beds may require some soil additions each year.
The remaining concern is sidewall construction. Nontreated wood won’t last long. Higher walls require thicker sidewalls. Treated wood is, by and large, not recommended due to leaching of chemicals into the vegetables. There are a few treated woods that are acceptable and fabricated wood, including concrete wood.
